The Atlantic Multi-decadal Oscillation (AMO) has been identified as a coherent mode of natural variability occurring in the North Atlantic Ocean with an estimated period of 60-80 years. It is based upon the average anomalies of sea surface temperatures (SST) in the North Atlantic basin, typically over 0-80N. To remove the climate change signal from the AMO index, users typically detrend the SST data at each gridpoint or detrend the spatially averaged time series. Trenberth and Shea (2006) recommend that the detrending be done by subtracting the global-mean SST anomaly time series from the spatially averaged time series. See the Expert Guidance by Dr. Kevin Trenberth for the rationale for the global-mean detrending approach. The Expert Guidance by Dr. Rong Zhang discusses the impacts and mechanisms of the AMO.